-LRB- CNN -RRB- -- Eight-time gold medal winner at the Beijing Olympics and multiple world-record holder Michael Phelps warmed up for the Swimming World Championships in Rome by setting a new men 's world record in the 100 meters butterfly .

Michael Phelps attacks the pool in Indianapolis to set a new world mark in the 100m fly .

The 24-year-old American shaved 18-hundredths of a second from the previous mark set by compatriot Ian Crocker in 2005 , with a time of 50.22 on the third day of competition at the U.S. National Championships in the Indianapolis .

`` I was pretty happy with my swim . I really wanted to break 50 seconds , but that is something to shoot for , '' Phelps told the event 's official Web site .

`` Ian Crocker texted me after prelims . He wished me all the luck . That really meant a lot to me as a competitor and as a friend , '' he added .

The new time takes Phelps 's personal tally of individual world records to five , to add to the three he can claim from relay events , and means he has qualified for three events at the upcoming World Championships in Rome thus far .

Places were booked with wins in the 200m freestyle and 200m butterfly on Wednesday while a further slot could be confirmed via the 100m freestyle .

Phelps , who was banned for three months when he was pictured smoking drugs at a party after returning from Beijing , has been eager to regain his Olympic form after his enforced exile from the pool .

`` This is something that I really , really wanted to accomplish , '' Phelps told the LA Times . `` Crock and I had a lot of great history , a lot of great races with one another . I 've wanted that record ever since he took it in '03 worlds ... . After the race , you could tell I was pretty fired up and excited . ''

Elsewhere , twelve-time Olympic medallist Dara Torres qualified for the World Championships team in the 50m freestyle .

The American told the LA Times there was still work to do despite the result : `` My coach was telling me I probably lost four or five tenths -LSB- of a second -RSB- on the start , '' said Torres .

`` The adrenaline kind of took over so I did n't really feel -LRB- my knee injury -RRB- . It 's a great feeling to be able to be out there and still race -LSB- at age 42 -RSB- , but that time wo n't medal at the world championships , '' Torres added .

The men 's 50m freestyle saw four Olympians battled for the gold , with Nathan Adrian beating his 2008 Olympic teammates Cullen Jones and Garrett Weber-Gale by 0.3 seconds .

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Michael Phelps sets new men 's 100m fly world record time of 50.22

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The American has now qualified for three events at the World Championships

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Phelps , 24 , now holds five personal world records in the pool

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New time went better than the mark set by compatriot Ian Crocker in 2005